This invention relates to improved freeze protected, air-cooled, vacuum steam condensers serving steam turbine power cycles or the like and, more particularly, to improved apparatus for condensing steam or other vapors in extremely cold climates and draining the condensate over a wide range of steam loads, steam pressures and ambient air temperatures and for also completely removing the steam-transported, undesirable, non-condensible gasses that migrate and collect in the rear headers of the steam condensing tube bundles.